Flotation is a physical separation process for separating mixtures of fine-grained solids. such as ores and gangue, in an aqueous froth or suspension with the aid of air bubbles as a result of a different surface wettability of the particles contained in the suspension. They are used for preparing natural resources and for processing preferably mineral materials with a low to medium content of a useful components or a recyclable material, for example in the form of non-ferrous metals, iron, metals of the rare earths and/or noble metals as well as non-metallic natural resources.
Pneumatic flotation machines are known. WO 2006/069995 A1 describes a flotation machine with a housing comprising a flotation chamber, with at least one nozzle arrangement, referred to here as ejectors, also with at least one gassing device, referred to as aerating devices or aerators when air is used, as well a collecting container for foam product formed during the flotation.
DE 33 12 070 A1 describes a flotation cell, in which the gassing of the cloudy material is undertaken by gassing outside the cloudy material, with the inflow direction of the aerated cloudy material able to changed in the vertical and/or lateral direction.
German patent No. 726 709 describes a facility for pneumatic foam-flotation processing of ores, coal and other minerals in which height-adjustable air supply pipes are present.
In pneumatic flotation a suspension of water and fine-grain solid material mixed with reagents is generally introduced via at least one nozzle arrangement into a flotation chamber. The intended effect of these reagents is that especially the valuable particles to be separated by preference are embodied hydrophobically in the suspension. Simultaneously with the suspension the at least one nozzle device is supplied with gas, especially air, which comes into contact with the hydrophobic particles in the suspension. The hydrophobic particles adhere to the gas bubbles that form, so that the gas bubble structures, also called aeroflakes, float and form the foam product on the surface of the suspension. The foam product is discharged into a collecting container and usually concentrated further.
It has been shown that the quality of the foam product or the separation success of the method of pneumatic flotation depends inter alia on the probability of a collision between a hydrophobic particle and a gas bubble. The higher the probability of collision, the greater is the number of hydrophobic particles that adhere to a gas bubble, rise to the surface and form the foam product together with the particles.
One of the factors influencing the probability of a collision is the position of the at least one gassing device in the flotation chamber. In this case the optimum position has previously been selected once as a function of the properties of the suspension used, such as a volume concentration of solids, an ore content, a mineral composition, a particle size distribution etc., as well as the flow conditions in the flotation chamber, and retained over the operating life of the flotation machine.
It has now been shown that these influencing variables change frequently even during the operating life, so that the one-time selection of the position of the at least one gassing device no longer corresponds to the optimum position and the quality of the foam product or the separation performance reduces or fluctuates.
Therefore one of the options previously employed was to change a delivery amount or type of reagents in order to counter a change in the influencing variables. These measures are however only suitable to a restricted extent for maintaining the quality of the foam product or the separation success.